1. Field of the Invention
This invention relates to rearview mirrors for vehicles, and more particularly to a rearview mirror to absorb the incident light by using a liquid crystal of negative dielectric anistropy mixed with a blue dye by 2%.
2. Description of the Prior Art
When vehicles are driven at night, the drivers are dazzled by the light beams reflected into the sight from the headlights of following vehicles by the rearview mirrors. In order to prevent such dazzling of reflected light, rearview mirrors must be improved.
In the beginning, as the means for attenuating the reflections of light had been mainly used polarizers, color filters, and prisms together with a method of scattering light by means of an uneven reflecting surface.
However, since such a rearview mirror essentially attenuates the incident light to a certain level or otherwise, reflects the incident light toward a certain direction, the image of an object projected on the mirror is always not clear, false images are generated, etc., thereby making its practical use impossible.
Recently, a rearview mirror using a liquid crystal device having light absorption property is attracting attention. In this construction, a liquid crystal device is incorporated into the rearview mirror so that the orientations of the liquid crystal molecules are changed to absorb light when the amount of the light incident on the mirror exceeds a certain limit.
The liquid crystal used in the mirror said above is such a kind that a dichromatic dye mixes with a nematic liquid crystal of positive or negative dielectric anisotropy.
The nematic liquid crystal of positive dielectric anisotropy and the nematic liquid crystal of negative dielectric anisotropy are oriented parallel with the electrodes and absorb light respectively with the voltage not applied and with the voltage applied. Hence, the nematic liquid crystal of positive dielectric anisotropy should be always supplied with the voltage to keep its orientation perpendicular to the electrode, thereby resulting in high consumption of power and its life becoming short. On the other hand, the nematic liquid crystal of negative dielectric anisotropy seems to be the most suitable in view of power consumption and life, but it has the problem that the initial operating voltage is relatively high and the projected image becomes unclear owing to low on-off contrast ratio.
Furthermore, the life of a liquid crystal is impaired by ultraviolet rays, which causes the dichromatic dye of the liquid crystal to undergo chemical reaction and to be disqualified.
Further, because the vertical orientation films are not electrically insulated, electric currents flow between the electrodes due to the conductive impurities intervening into the liquid crystal during the manufacture, thereby resulting in shortcomings.
Besides, since glasses are much used in the mechanism employing the liquid crystal device, considerable fragments are scattered when the mirror is fragmentized, thereby causing safety problems.